1. Field of the Invention
The present invention relates to an electronic information recording element-embedded reversible thermosensitive recording medium in which, even when image erasure/formation is performed at high speed, white voids and color fading do not occur in the formed image areas each corresponding to the surrounding area of an electronic information recording sheet, to an electronic information recording element, to an antenna circuit and to a conductive member; and image erasure can be completely performed.
2. Description of the Related Art
IC cards have been increasingly being used in various aspects from users' daily lives to business activities. Actually, they are used as various cards (e.g., cash cards, credit cards, prepaid cards and ETC cards (electronic toll collection system)); in transportation facilities (e.g., railways and buses); as affiliate cards for digital broadcasting, 3rd generation mobile phones, etc.; in library service counters; and as student ID cards, employee ID cards, basic resident register cards, etc. Meanwhile, the amount of IC cards disposed of has been being increasing in accordance with diversification of the current economic and social activities.
In view of this, there is a keen need to create a recycling society, where material consumption is reduced and less environmental load is given, by reconsidering the current economic societies and lifestyles involving mass production, mass consumption and mass disposal to promote effective utilization and recycling of materials.
As one promising measure, electronic information recording element (hereinafter may be referred to as an “IC chip module” or “IC chip”)-embedded reversible thermosensitive recording media can be used for reducing the amount of products disposed of. This is because they can rewrite information stored in the IC chip and show information as a visible image on their surface.
Such IC chip module-embedded reversible thermosensitive recording media have been used in the manufacturing industry as instruction sheets such as operation sheets, parts management sheets and process management sheets. Actually, there is repeatedly performed a cycle including winding an instruction sheet around a rod-like part or inserting it into a card case, washing stains on the instruction sheet, and rewriting the content of the instruction sheet using a printer.
When an image is formed on or erased from it, a heating tool (e.g., thermal head, erase bar, erase roller and erase plate) of the printer is pressed against the instruction sheet. Thus, rewriting of the instruction sheet must be performed so as not to break the IC chip module and not to avoid outflow of an adhesive agent from an adhesive portion between the IC chip module and the reversible thermosensitive recording medium. Also, washing of the instruction sheet must be performed so that the IC chip module is not peeled off from the reversible thermosensitive recording medium. Furthermore, desirably, the instruction sheet is flexible and shows a high-quality image.
For example, Japanese Patent Application Laid-Open (JP-A) Nos. 11-154210, 2000-94866, 2000-251042, 2001-63228 and 2002-103654 disclose IC cards as shown in FIG. 1 including, as an over sheet, a reversible thermosensitive recording sheet 114 having at least one reversible thermosensitive layer 114b containing an intrinsically colorless or light-colored leuco dye and a reversible color developer allowing the leuco dye to develop color through application of heat and to erase the developed color through next application of heat, and including, as the other over sheet, a base film 111 in which an IC card having an IC chip module 112 is embedded, wherein a core member 113 is formed between these two over sheets through injection molding so that these are thermally bonded via the core member 113 to each other.
In the above-described IC cards, the IC chip module 112 is provided so as to face the reversible thermosensitive recording sheet 114 and thus, the reversible thermosensitive recording medium is ununiformly pressed due to the IC chip module 112, whereby concavo-convex portions are undesirably formed on the recording medium. The reversible thermosensitive recording medium having the concavo-convex portions cannot be uniformly heated using a heating tool and thus, heat cannot be uniformly conducted in the reversible thermosensitive recording medium when image formation is performed. As a result, an uneven image is formed on the reversible thermosensitive recording medium. Also, when image erasure is performed, a heating tool is ununiformly pressed against the reversible thermosensitive recording medium, leading to failure in image erasure. Furthermore, the reversible thermosensitive recording medium has, on the surface thereof, a convex portion corresponding to the IC chip module 112. As a result, a heating tool is pressed via the reversible thermosensitive recording medium against the IC chip module 112, causing a problem in that the IC chip module 112 is damaged or peeled off from the reversible thermosensitive recording medium.
In view of this, for example, JP-A Nos. 11-91274, 11-59037, 11-85938, 2002-117880, 2003-141486 and 2003-141494 discloses countermeasures against the above problems. IC chip module-embedded reversible thermosensitive recording media disclosed in these Patent Literatures, however, have low flexibility and high rigidity (i.e., large thickness and high hardness).
JP-A Nos. 2005-250578 and 2006-344207, therefore, disclose reversible thermosensitive recording media in which an IC chip module is provided on an IC chip substrate disposed over a reversible thermosensitive recording sheet so that the IC chip module does not face the recording sheet. However, on the surface of an electronic information recording sheet having an electronic information recording element, an antenna circuit and a conductive member (hereinafter the electronic information recording sheet may be referred to as an “inlet”), concavo-convex portions are formed not only by the electronic information recording element but also by the antenna circuit and the conductive member. In this antenna circuit, a conductive member connects a front face of the antenna circuit board, in which surface an antenna circuit is formed, to a back face thereof to form a jumping circuit. When these front and back faces are penetrated using a laser, etc. for conduction, so-called caulking portions are formed. These caulking portions and the conductive member formed on the back face form concavo-convex portions on the electronic information recording sheet. Thus, as described above, even if only the IC chip is provided on the IC chip substrate over the reversible thermosensitive recording sheet so that the IC chip does not face the recording sheet, concavo-convex portions are formed on the reversible thermosensitive recording sheet. In particular, JP-A No. 2006-344207 describes that an antenna circuit board 2 has, on its back face, an electrically short-circuited jumper wire 12. However, also when the jumper wire 12 is formed on the reversible thermosensitive recording sheet side, the reversible thermosensitive recording medium problematically involves failures in image formation/erasure.
In order to solve the above-described problems, the present inventor has previously filed JP-A Nos. 2008-162077 and 2008-229911. In these Patent Literatures, an electronic information recording element is housed in a through hole of a sheet so as not to project from the sheet; and a face of the reversible thermosensitive recording sheet, on which face no reversible thermosensitive recording layer is provided, is made to face a face of the electronic information recording sheet, on which face none of an antenna circuit board, an electronic information recording element, antenna circuit and a conductive member is provided. In the reversible thermosensitive recording media having such a configuration, failure in image formation/erasure can be overcome when the transfer speed of a printer used is 2 IPS. However, when the reversible thermosensitive recording media undergo image erasure/formation at high speed (3 IPS or higher), a rewritten image cannot be improved in its qualities (i.e., involves color fading and incomplete erasure) in an area corresponding to the electronic information recording sheet (including areas each corresponding to an IC chip, an antenna circuit and a conductive member), leading to failure in color development.
Hitherto, the present inventor carried out studies on improvement in qualities of a rewritten image area corresponding to an electronic information recording sheet when the transfer speed of a printer used is 2 IPS, and has found that when image erasure/formation is performed at a transfer speed of 3 IPS, a rewritten image cannot be improved in its qualities. This is because the higher the transfer speed of the printer, the more difficult it is that heat applied from the erasure head is conducted in the reversible thermosensitive recording medium. When a temperature for image erasure is increased for improving erasability, the reversible thermosensitive recording medium is excessively heated by the erasure head. In this state, when image formation is performed, the reversible thermosensitive recording medium cannot be rapidly cooled to prevent color development (to be in an erasure mode).
When the electronic information recording sheet has, on a surface thereof, height differences and concavo-convex portions (i.e., the electronic information recording sheet does not have a flat surface and has concavo-convex portions in which the height from the top surface to the base portion is about 50 μm and which are formed by the IC chip, the antenna circuit, and the caulking portion connecting the antenna circuit to the IC chip), a thermal head insufficiently comes into contact with a surface of the reversible thermosensitive recording medium and thus, heat is not sufficiently conducted in the surface thereof due to the heat insulating effect of air. As a result, the reversible thermosensitive recording medium cannot be rapidly cooled, causing failure in color development.
Under such circumstances, demand has arisen for a high-quality electronic information recording element-embedded reversible thermosensitive recording medium in which, even when image erasure/formation is performed at a high speed of 3 IPS or higher, white voids and color fading do not occur in the formed image areas each corresponding to the surrounding area of the electronic information recording sheet, to the electronic information recording element, to the antenna circuit and to the conductive member; image erasure can be completely performed; and no lamination displacement occurs.